This invention relates to galvanic protection of elongated steel articles by attaching a wire or strip of a sacrificial metal or metal alloy along the length thereof, and more particularly, relates to the galvanic protection of a reinforcing steel bar by providing a zinc wire attached to the length of the reinforcing steel bar and to the product produced thereby.
Corrosion and deterioration of reinforced concrete on bridge decks, support columns and parking structures is a problem of increasing significance in terms of cost of repair and safety. The permeable nature of concrete eventually allows water and sodium chloride from road salt to enter the concrete structure and chemically react with the reinforcing steel to cause corrosion. In the first stages of iron corrosion, de-adhesion occurs at the iron/concrete interface. As corrosion continues, the iron corrosion products expand causing delamination, cracking and significant weakening of the concrete structure.
In an attempt to inhibit rebar corrosion in reinforced concrete many methods and procedures have been proposed. German Patent No. 2,944,878 discloses a method whereby reinforcing steel bars (rebars) are tightly enclosed by a metal or plastic protective sheath. The impervious sheath of metal, synthetic resin or the like material prevents intimate contact of the rebar with water and corrosive salts, thus reducing the rate of corrosion of the rebar. In practice, especially with large diameter rebar, the placement of the rebar and the pouring of concrete often results in a nick or scrape of the protective coating of the rebar allowing the corrosive salts to react with the bare iron which consequently corrodes.
Preventing the ingress of water and salts into a concrete structure where they may react with the rebar has been attempted by means of an impermeable mastic coating applied to the concrete surface. Mastic coatings are generally not very durable and must be protected from vehicular traffic with a tough overlay material. Constant monitoring is also required to ensure a water-tight surface is provided.
U.S. Pat. No. 5,069,822 discloses a method to protect rebar from corrosion by using an impermeable membrane in combination with a cathodic protection system. The membrane material is made of chloroprene or polyurethane and can be overcoated by a wear layer.
Cathodic protection used in combination with the membrane above is known and similar to that of U.S. Pat. No. 4,496,444. A sacrificial anode in the form of a small block is in electroconductive communication with a surface such as iron to be protected. The sacrificial anode made of a material such as zinc has a greater potential to react chemically with salts or the like, thus corroding sacrificially while protecting the iron rebar.
The use of zinc for protection of rebar is also known in the form of galvanized rebar. In galvanizing, a thin continuous coating of zinc is provided on the complete steel surface, providing not only barrier protection but also galvanic protection to the rebar. It has been found that zinc may corrode inside concrete at a rate depending on ambient conditions. In regular hot-dipped galvanized rebar, the coating of zinc enveloping rebar is typically about 100 .mu.m in thickness. The corrosion of rebar steel will occur when this zinc coating is consumed.